The coagulation of blood is necessary to in order to stop both internal and external bleeding. However, it is often desirable to alter the natural coagulation characteristics of blood while performing certain medical procedures. For example, during such surgical procedures the uninhibited coagulation of the blood can cause blood clots which may result in severe medical complications to the patient. Thus, it is desirable to suppress the natural coagulation process during the surgical procedure. However, upon the completion of the surgical procedure, it is desirable for the patient's blood to regain its natural coagulation characteristics. As such, the blood will again be able to clot and heal incisions and stop any internal or external bleeding.
In an attempt to scientifically control the coagulation characteristics of a persons blood, pharmacological agents have been developed that modify the inherent ability for a patient's blood to clot. A common substance usd to prolong the clotting time of a patient's blood is heparin. Heparin is a naturally occurring polysaccharide sulfuric acid ester found especially in lung, liver and intestinal tissue and has the ability in certain circumstances to prolong the clotting time of blood. Commercially available heparin is derived from animal tissues principally porcine intestine or bovine lung. As presently understood, commercially processed heparin is complex substance and its pharmacological activity per unit weight may vary depending on the characteristics of a specific batch of material. Due to the inconsisting of commercially produced heparin, heparin is sold with its biological potency expressed in U.S.P. units, where U.S.P. units are related to the clot formation inhibition of heparin mixed with sheep plasma.
When the effects of heparin on a patient's blood is no longer desired, it is commonplace to administer a substance known as protamine to the heparinized patient. Protamines are simple strongly basic proteins of relatively low molecular weight. These proteins are water soluble, not coagulated by heat and yield only amino acids, chiefly arginine when hydrolyzed.
Protamine is a naturally occurring material and is commercially available to the medical profession as an extract from certain fish (salmon) tissue. The purity and therefore the physiological potency of commercial protamine preparations, for reasons not well understood, have been shown to vary from batch to batch. Protamine is dispersed on a weight basis. Protamine, while of different chemistry than heparin, also has the property of prolonging the blood clotting time in humans.
Heparin and protamine are reactive with each other on a stoichiometric basis. Heparin is an anionic substance and protamine is a cationic substance. When the two substance are mixed in blood (either in vivo or a test tube) they react quantitatively to form a neutral (and physiologically inactive) entity. Medical personnel therefore infuse protamine at the conclusion of a surgical procedure, to neutralize heparin in patient's blood and restore normal, baseline blood clotting ability.
Protamine, however, as previously discussed, is itself an anticoagulant and if excess protamine is infused, hemostasis will not be achieved. Further complications can result from the fact that protamine may be toxic to some individuals. Protamine is also reportedly capable of including an allergic response in certain patients.
Since the amount of heparin in a patient's blood is critical, and since heparin varies in potency from batch to batch and patient to patient, measuring an administered dosage is insufficient in predicting the clotability characteristics of a patient's blood caused by the heparin. Similarly, since the potency of protamine also varies from batch to batch and patient to patient, merely measuring the administered dosage does not predict the effectiveness of the protamine on a given patient. Consequently, since dosage measuring is inconclusive, the blood of a patient must be constantly monitored and tested in order to accurately determine the effects of administered heparin, protamine or like compounds on the coagulation characteristics of a patient's blood.
The prior art is replete with various apparatus and methods for measuring the coagulation time of blood samples. For example, a method and apparatus for detecting blood coagulation is shown in U.S. Pat. No. 4,797,369 which issued on Jan. 10, 1989, entitled METHOD AND APPARATUS FOR DETECTING A BLOOD CLOT to Michael Mintz, and assigned to the assignee herein. In that particular patent, there is disclosed the technique for measuring clot time whereby a sample of whole blood or blood plasma is dispersed into two or more zones. The zones are separated and brought together repeatedly, such that the blood sample is divided into multiple parts each associated with a zone. The parts are then rejoined into a single part and the process of separation and joining continues. During the process, a liquid bridge between the separated parties is initially supported by surface tension, but initially collapses at the point of maximum zonal separation. When a fibrin clot is entrained within the rejoined parts, it will align in a direction parallel to the direction of the relative motion between the zones. In this manner, a thread appears between the parts as they are being separated. This thread is indicative of a clot, which clot is capable of being detected by visual or electrical means.
U.S. Pat. No. 3,486,859 entitled BLOOD ANALYZING METHOD AND APPARATUS issued on Dec. 30, 1969 to R. Greiner et al. This patent depicts a blood analyzing method and apparatus including a double arm holder having blood liquid reactant chambers which communicate with each other via a small capillary conduit. An air pump is provided for applying pressure changes to one of the chambers to effect periodic mixing of the liquids via the capillary conduit. An indicator means are included to detect the progressive restriction of the capillary conduit upon coagulation of the blood.
U.S. Pat. No. 3,695,842 entitled METHOD AND SYSTEM FOR ANALYZING A LIQUID issued on Oct. 30,1972 to M. D. Mintz, and assigned to the assignee herein. The patent describes in detail a magnetically coupled mechanical blood clot detection system wherein a variable conductance device is disposed adjacent to a zone containing a liquid and member of ferromagnetic flux lines is formed between the zone and the member. A predetermined variation in the conductance of the device is detected upon change in the magnetic flux lines when the liquid transforms itself and the member is displaced. The signal is produced at the time the predetermined variation in conductance has been detected.
An improved system means for measuring clotting time is disclosed in U.S. Pat. No. 3,836,333 entitled "SYSTEM FOR TIMING THE COAGULATION OF BLOOD" issued to Michael D. Mintz, on Oct. 30, 1972 and assigned to International Technidyne Corporation, the assignee herein. An electromagnetic bias coil, which is wound around the reed switch, provides stead-state magnetic flux lines that supplement the flux lines provided by the permanent magnet. When the density of the flux lines passing through the reed switch decreases, as a result of the magnet being displaced, the reed switch opens. The bias coil also provides a magnetic pulse, which forces the reed switch to a closed state. This system is manufactured under the trademark HEMOCHRON by International Technidyne Corporation at Edison, N.J.
U.S. Pat. No. 3,890,098 entitle MACHINE FOR THE DETERMINATION OF PROTHROMBIN TIME AND P.T.T. issued on Jun. 17, 1975 to E. Moreno. This patent describes a reactive material which is placed in a cup which communicates with a second cup via a restricted orifice. Plasma is placed in the second cup and the reactive material and plasma are moved from cup to cup by a pump until coagulation of the plasma takes place. Means are then provided for stopping the motion of the mixture of reactive material and plasma. Other means are provided for measuring the time required for coagulation.
U.S. Pat. No. 3,951,606 entitled APPARATUS FOR PROTHROMBIN TESTING issued on Apr. 20, 1976 to R. Moyer et al. This patient shows manually operable, disposable device which can measure coagulation rates. The device is a tube of a uniform bore which can accommodate a sample and contains appropriate amounts of lyophilized reagents required to conduct individual tests such as that for prothrombin time. Calibration marks on the tube are correlated in terms of these times and the position in which a liquid sample becomes immobilized as it descends down the tube corresponds to the test time. The rate of descent of the liquid is controlled by a limiting orifice or constriction or by inclining the tube to the vertical axis.
U.S. Pat. No. 4,197,734 entitled APPARATUS FOR DETERMINING BLOOD CLOTTING TIME issued on Apr. 15, 1980 to A. Rosenberg. This patent describes an apparatus which is capable of determining the clotting time of blood. The apparatus includes a support frame which supports a syringe containing a blood sample and a turntable adapted to rotate at a normal rate of speed. Blood from the syringe drops onto the turntable where the clotting time is automatically and graphically depicted by a chart rotatively carried upon the turntable. The apparatus can also be employed to determine variations in the viscosity of blood plasma and other fluids.
U.S. Pat. No. 4,725,554 entitled METHOD FOR MEASURING BLOOD COAGULATION TIME issued on Feb. 16, 1988 to K. Schildkenecht. This patent shows a method for measuring the coagulation time of a blood sample, in which a sample reagent mixture is formed by introducing the sample and at least one reagent into a cuvette. The sample reagent mixture is moved in a stationary cuvette so that the mixture flows back and forth around an edge projecting in to the cuvette whereby a clot forms and is detected on this edge.
U.S. Pat. No. 4,659,550 entitled METHOD AND APPARATUS FOR MEASURING BLOOD COAGULATION TIME is the parent of U.S. Pat. No. 4,725,554 and essentially describes the same system further utilizing photocell detectors to determine a clot formation.
As one can see from the above, there are may different types of systems all of which are operative to detect the formation of a clot and to provide an indication of coagulation time. However, many of the prior art devices are complicated and difficult to manufacture. As such, it is a primary objective of the present invention to provide a blood clot detection apparatus and method which is extremely simple to utilize and which is associated with a disposable covette to enable a plurality of such tests to be performed at low cost.